The Gnome GUI (gnome-shell) only lets you set a single shortcut key. Can you for instance set Super+Tab and Alt+Tab to both switch applications?
Yes, you can. This is verified to work on Ubuntu 20.10 and 21.04RC.
The following commands acheive the requested outcome:
gsettings set org.gnome.desktop.wm.keybindings switch-windows-backward "['<Shift><Super>Tab', '<Shift><Alt>Tab']"
gsettings set org.gnome.desktop.wm.keybindings switch-windows "['<Super>Tab', '<Alt>Tab']"
For more options see here:
# list all keybindings
gsettings list-recursively | grep -e org.gnome.desktop.wm.keybindings -e org.gnome.settings-daemon.plugins.media-keys -e org.gnome.settings-daemon.plugins.power | sort
# confirm no other keybinding conflicts
gsettings list-recursively | grep '<Control>1'
# set multiple keybindings for "Switch to Workspace 1"
gsettings set org.gnome.desktop.wm.keybindings switch-to-workspace-1 "['<Super>Home', '<Control>1']"
# confirm value is set correctly
gsettings get org.gnome.desktop.wm.keybindings switch-to-workspace-1
from here.